The present invention relates generally to improvements in electric motors and more particularly to an improved permanent magnet rotor electric motor in which cogging is minimized.
An important problem encountered in the operation of conventional electric motors and particularly AC motors with permanent magnet rotors, is that of cogging--that is, the presence of non-linear magnetic rotational forces. The presence of appreciable amounts of cogging significantly reduces the efficiency, reliability and uniform operation of the motor. Numerous expedients have been employed to reduce the cogging in electric motors, including that of skewing the stator, using an odd number of winding housing slots relative to the product of the number of phases and magnetic poles, as well as the skewing of the rotor magnets. However, these expedients possess many drawbacks and disadvantages, are awkward and inconvenient, are of limited application and effectiveness and otherwise leave much to be desired.